Biomass, horizontal zonation and vertical stratification of polychaete fauna in the littoral sediment of Cochin estuarine mangrove habitat, south west coast of India

Biomass distribution, horizontal zonation, relative dominance and vertical distribution of polychaetes were studied. Highest biomass was recorded in the mid tidal re-ion in both study areas. The monthly values varied from 4.43 to 128.28 g.m(-2) at st 1 and 2.57 to 67.31 g.m(-2) at st 2. Multiple regression analysis between biomass and environmental parameters indicate that they could not individually or in combination bring about the spatial and temporal variability in biomass distribution. Moreover, at st 1 edaphic factors appear to be responsible for partial variation in biomass indicating comparatively high F ratio for variance analysis than station 2. ANOVA of species diversity indices values (P < 0.5) between the three tidal regions showed a clear horizontal zonation of polychaetes, especially at st 1. A substantial difference in percentage composition of fauna, up to 15 cm depth of mangrove soil, was found in all the three tidal zones studied. This variability in the community structure in the top (0-5 cm) and deeper mangrove sediment (10-15 cm) is pertained to a variety of characteristic features of both upper and deeper sediments. High numerical abundance and coexistence of certain euryhaline species showed significant similarity index (>70%) among polychaete fauna. This similarity and affinity of fauna for a long period evidently indicate the habitat stability that is pertained to the existence of species diversity and abundance. This is related to the prolonged food resource input and profound standing capacity in the littoral mangrove soil, which virtually render in building up a stable community structure of polychaetes. As a result of this, selection of habitat by polychaetes, its survival and subsequent long-term biomass production were occurred. The strong similarity of polychaete fauna between months and biomass productivity can be considered for deriving the productive characteristic of the mangrove habitat, and also for assessing demersal fishery potential.